The interaction of electric field and hydrostatic pressure in an electrical double layer: A simple “first principle” model that accounts for the finite sizes of counterions

A simple model describing the influence of ion size in the electrical double layer (EDL) near a highly charged plane is proposed here. This model is based on the Poisson–Boltzmann equation with a single additional term representing the mechanical response of bulky ions to hydrostatic pressure. This pressure is produced by Coulomb forces, and increases to several kilobars in the vicinity of a highly charged plane. Numerical simulations demonstrate close packing as a limit for counterion concentrations. Differential capacity reaches maximum at 0.1–0.3 V and remains reasonably small in wide range of potentials.

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